This application is not related to any pending United States or international patent application.
This application is not referenced in any Microfiche Appendix.
1. Field of the Invention
This invention relates solid state electronic apparatus, and particularly to a solid state circuit for providing a pre-selected low AC voltage output from a variable AC voltage input. The invention is particularly adapted for control of low voltage lighting circuits.
2. Background of the Invention
In many applications of electronic circuits, it is important to provide a pre-selected AC voltage output that is independent of an AC voltage input. Most particularly, IT is important to be able to provide a pre-selected AC voltage output from an AC voltage input employing only solid state, inexpensive, dependable, and readily available circuit components.
The invention herein is applicable to any installation in which a pre-determined regulated AC output voltage is required when a variable AC input voltage is available and wherein the input voltage always exceeds the desired output voltage. The invention is particularly useful in low voltage wiring. A typical application of low voltage wiring is in landscaped lighting, such as the provision of lights along a sidewalk, a driveway, a flower bed, or to highlight statuary, shrubbery, or the like. Such landscape lighting can be installed by home owners, or by professional installers. For this reason, the electrical codes of many municipalities allow non-licensed electricians to install low voltage lighting so as to alleviate the expense of employing licensed electrical contractors to do such work. The rationale for permitting home owners to install their own low voltage lighting is that the voltage is such that the possibility of receiving a lethal, a harmful, or even a painful electric shock is substantially eliminated. Thus, if a home owner that is inexperienced with installing electrical wiring elects to install his own low voltage wiring system, he can do so with safety since the voltage that is transmitted to the wiring apparatus is typically below 15 volts, and further typically employs circuitry with nominal maximum amperage so that the possibility of causing a fire or an injurious exposure to electricity is substantially non-existence.
One of the problems encountered in low voltage wiring is that of maintaining a pre-selected AC voltage at different locations when distances from a household AC outlet can vary considerably. Typically, a low voltage wiring system consists of a transformer having a primary that is connectable to the typical household voltage, that is, in the United States, 110 volts. The transformer serves to step the voltage down so that the voltage output is at a relatively low voltage, such as a maximum of 15 volts or similar low voltages according to electrical code requirements. This low voltage, such as 15 volts, is then fed to lighting fixtures. Some of the lighting fixtures may be relatively close to the transformer so that very little voltage drop occurs between the transformer and the energy consuming light fixture. On the other hand, some of the outdoor lights may be at a substantial distance, such as several hundred feet from the transformer that supplies the low voltage. The use of low voltage mandates greater current flow in order to illuminate electric bulbs of typical wattages, that is, the current in a low voltage wiring system is usually substantially greater than the current that would be required if the lighting was all powered by standard household voltage. High current flow causes rapid voltage drops through wiring required to reach lighting fixtures at a distance. For this reason, it is very helpful if means can be provided so that a variety of light fixtures or circuits extending to light fixtures, spaced at a distance from an AC input source can be operated in such a way that substantially the same voltage appears across each light bulb irrespective of its distance from the initial voltage source.
Accordingly, one of the objectives of the present invention is to provide a solid state device for producing a predetermined AC voltage output, irrespective (within limits) of the AC voltage input. By the expression xe2x80x9cirrespective of AC voltage inputxe2x80x9d means that the AC voltage input cannot vary indefinitely. In a preferred practice of the invention, the input voltage is slightly (within a few volts) above the desired output voltage. The regulator of this invention then provides a slightly reduced, but predetermined output voltage wherein the reduced output voltage is that which is preferred for operating light fixtures or other load consuming devices.
For reference to previously issued patents relating to systems for providing low voltage wiring and for assistance in providing solid state voltage regulators, reference may be had to the following previously issued United States patents:
This invention herein provides a circuit having an AC input such as an input of approximately 15 volts to provide a preselected output voltage of, as an example, 12 volts. The United States is 120 volts AC voltage down to a substantially lower but preselected voltage, such as 24 volts AC.
The invention herein provides a preselected output voltage equal to or less than an input voltage. As an example of the application of the invention to low voltage lighting, the system may use, as an example, a transformer that reduces household current from the typical 110 volts AC to 15 volts AC. Bulbs employed in a lighting system may be designed to operate efficiently at 12 volts AC. In a lighting circuit, voltage drops always occurs between the AC input circuit and light bulbs in various distances from the voltage source. However, it is important that the voltage supplied to the various bulbs employed in a wiring circuit be as near as possible to the same voltage, such as 12 volts. Thus, circuits having light bulbs close to the voltage source may be the same as the input voltage, such as 15 volts. However, in a location at a farther distance from the source, the voltage may drop to 14 volts. Farther away from the voltage source, the voltage may drop to, as an example, 13 volts due to I2R loss because of the length of the wiring. However, the voltage to the bulbs needs to be at or close to 12 volts.
The solid state voltage regulator of this invention can be used at a plurality of locations at various distances from an AC source, and therefore, at distances wherein the I2R drop reduces the available voltage at the point of a circuit in a manner that, nevertheless, all points in the circuit have available for illumination of bulbs a preselected standardized voltage, such as 12 volts. As previously indicated, the application of this invention to low voltage wiring is merely an example. The invention is in no wise limited to this specific application.
A more complete understanding of the invention will be obtained from the following specification of the preferred embodiment, taken in conjunction with the attached drawings and the claims.